When the oculomotor system is in complete equilibrium, the two separated eyes can become the same functional unit and no deviation occurs, which is called orthophoria. If the central control is out of balance, the strength of the extraocular muscles is not balanced, the two eyes cannot look at the target at the same time, the visual axis is separated, one eye looks at the target, the other eye deviates from the target, called strabismus. The harm of strabismus: 1. destroys the normal binocular vision, loses the stereo vision function, and affects the further education and employment. 2.Produce amblyopia, if not treated in time, resulting in lifelong visual disability. 3. Affects aesthetics and creates mental health problems such as low self-esteem.